<template>
  <div class="spec-preview" @mousemove="move">
    <!-- 使用一个变量，从数组身上获取值，方便后期点击小图时，同步切换大图 -->
    <img :src="img.imgUrl" />
    <div class="event"></div>
    <div class="big">
      <img :src="img.imgUrl" ref="bigImg"/>
    </div>
    <div class="mask" ref="mask"></div>
  </div>
</template>

<script>
export default {
  name: "Zoom",
  data() {
    return {
      defaultIndex: 0,
    };
  },
  props: ["skuImageList"],
  mounted() {
    // 根据小图列表选中的图片，同步修改zoom组件中的图片展示
    this.$bus.$on("changeDefaultIndex", (index) => {
      this.defaultIndex = index;
    });
  },
  computed: {
    img() {
      // 从skuImageList这个数组身上读取到的以一个元素 是一个对象，当数据未获取到时，读取的结果是undefined 从undefined身上读取值，会报错 所以设置默认值为{}
      return this.skuImageList[this.defaultIndex] || {};
    },
  },
  methods: {
    move(e) {
      // 获取mask和大图
      let mask = this.$refs.mask;
      let bigImg = this.$refs.bigImg;
      // 获取鼠标位置
      let mouseX = e.offsetX;
      let mouseY = e.offsetY;
      // 蒙版移动得距离
      // 鼠标位置-蒙版宽度一半
      let moveX = mouseX - mask.offsetWidth / 2;
      let moveY = mouseY - mask.offsetHeight / 2;
      // 水平边界值判断
      if (moveX < 0) {
        //左侧
        moveX = 0;
      } else if (moveX > e.target.offsetWidth - mask.offsetWidth) {
        //右侧
        moveX = e.target.offsetWidth - mask.offsetWidth;
      }
      // 垂直边界值判断
      if (moveY < 0) {
        //上侧
        moveY = 0;
      } else if (moveY > e.target.offsetHeight - mask.offsetHeight) {
        //下侧
        moveY = e.target.offsetHeight - mask.offsetHeight;
      }
      // 赋值给蒙版得left和top
      mask.style.left = moveX + "px";
      mask.style.top = moveY + "px";
      // 不光蒙版动 大图也得跟着动
      bigImg.style.left = -2 * moveX + "px";
      bigImg.style.top = -2 * moveY + "px";
    },
  },
};
</script>

<style lang="less">
.spec-preview {
  position: relative;
  width: 400px;
  height: 400px;
  border: 1px solid #ccc;

  img {
    width: 100%;
    height: 100%;
  }

  .event {
    width: 100%;
    height: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: 998;
  }

  .mask {
    width: 50%;
    height: 50%;
    background-color: rgba(0, 255, 0, 0.3);
    position: absolute;
    left: 0;
    top: 0;
    display: none;
  }

  .big {
    width: 100%;
    height: 100%;
    position: absolute;
    top: -1px;
    left: 100%;
    border: 1px solid #aaa;
    overflow: hidden;
    z-index: 998;
    display: none;
    background: white;

    img {
      width: 200%;
      max-width: 200%;
      height: 200%;
      position: absolute;
      left: 0;
      top: 0;
    }
  }

  .event:hover ~ .mask,
  .event:hover ~ .big {
    display: block;
  }
}
</style>